twenty five http:// nisee.berkeley.edu/godden concrete - - PowerPoint PPT Presentation

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F2009abn

twenty five

concrete construction:

flat spanning systems

Concrete Spans 1 Lecture 25 Architectural Structures ARCH 331

lecture

http:// nisee.berkeley.edu/godden

ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN

ARCH 331

• DR. ANNE NICHOLS

SPRING 2019

Concrete Spans 2 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

• economical & common
• resist lateral loads

Concrete Spans 3 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

• flat plate

– 5”-10” thick – simple formwork – lower story heights

• flat slab

– same as plate – 2 ¼”–8” drop panels

Concrete Spans 4 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

• beam supported

– slab depth ~ L/20 – 8”–60” deep

• one-way joists

– 3”–5” slab – 8”–20” stems – 5”-7” webs

The Architect’s Studio Companion

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Concrete Spans 5 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

• two-way joist

– “waffle slab” – 3”-5” slab – 8”-24” stems – 6”-8” webs

• beam supported slab

– 5”-10” slabs – taller story heights

F2008abn Concrete Spans 6 Lecture 25 Foundations Structures ARCH 331

Reinforced Concrete Design

• simplified frame analysis

– strips, like continuous beams

• moments require

flexural reinforcement

– top & bottom – both directions of slab – continuous, bent or discontinuous

Concrete Spans 7 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

• one-way slabs (wide beam design)

– approximate analysis for moment & shear coefficients – two or more spans – ~ same lengths – wu from combos – uniform loads with L/D  3 –  n is clear span (+M) or average of adjacent clear spans (-M)

Concrete Spans 8 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

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F2008abn Concrete Spans 9 Lecture 25 Architectural Structures ARCH 331

Reinforced Concrete Design

• two-way slabs - Direct Design Method

– 3 or more spans each way – uniform loads with L/D  2 – rectangular panels with long/short span  2 – successive spans can’t differ > longer/3 – column offset no more than 10% span

Concrete Spans 10 Lecture 25 Foundations Structures ARCH 331 F2008abn

Reinforced Concrete Design

Concrete Spans 11 Lecture 25 Foundations Structures ARCH 331 F2008abn

Shear in Concrete

• at columns
• want to avoid

stirrups

• can use shear

studs or heads

Concrete Spans 12 Lecture 25 Foundations Structures ARCH 331 F2008abn

Shear in Concrete

• critical section at d/2 from

– column face, column capital or drop panel

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F2008abn Concrete Spans 13 Lecture 25 Foundations Structures ARCH 331

Shear in Concrete

• at columns with waffle slabs

http:// nisee.berkeley.edu/godden Concrete Spans 14 Lecture 25 Foundations Structures ARCH 331 F2008abn

Openings in Slabs

• careful placement of holes
• shear strength

reduced

• bending &

deflection can increase

Concrete Spans 15 Lecture 25 Foundations Structures ARCH 331 F2008abn

General Beam Design

• f’c & fy needed
• usually size just b & h

– even inches typical (forms) – similar joist to beam depth – b:h of 1:1.5-1:2.5 – bw & bf for T – to fit reinforcement + stirrups

• slab design, t

– deflection control & shear

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2

bh S 

Concrete Spans 16 Lecture 25 Foundations Structures ARCH 331 F2008abn

General Beam Design (cont’d)

• custom design:

– longitudinal steel – shear reinforcement – detailing

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Concrete Spans 17 Lecture 25 Foundations Structures ARCH 331 F2008abn

Space “Frame” Behavior

• handle uniformly distributed loads well
• bending moment

– tension & compression “couple” with depth – member sizes can vary, but difficult

Concrete Spans 18 Lecture 25 Foundations Structures ARCH 331 F2008abn

Space “Frame” Behavior

• shear at columns
• support conditions still important

– point supports not optimal

• fabrication/construction can dominate

design

Concrete Spans 19 Lecture 25 Foundations Structures ARCH 331 F2008abn

Folded Plates

• increased bending stiffness with folding
• lateral buckling avoided

F2008abn Concrete Spans 20 Lecture 25 Foundations Structures ARCH 331

Folded Plates

• common for roofs
• edges need

stiffening

http:// nisee.berkeley.edu/godden

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F2008abn Concrete Spans 21 Lecture 25 Foundations Structures ARCH 331

Folded Plates

– State Farm Center (Assembly Hall), University of Illinois – Harrison & Abramovitz 1963 – Edge-supported dome spanning 400 feet wound with 614 miles of one-fifth inch steel wire

www.library.illinois.edu